1. Field of the Invention
The present invention relates to a printer having a platen, and a print head disposed opposite to the platen, for printing on a recording medium such as a cut sheet or envelope supported on the platen.
2. Discussion of the Prior Art
A known printer of the type indicated above is equipped with adjusting means for adjusting a clearance between the surface of the platen and the print head, so that a gap between the recording surface of the recording medium and the end face of the print head is maintained at a predetermined constant value, irrespective of the thickness of the medium.
However, the above type of known printer suffers from a problem when a printing operation is conducted on an outer surface of an envelope as shown in FIG. 6, with a predetermined constant gap D1 provided between the printing surface of the envelope and the print head. More specifically, the envelope may have an overlapping portion which consists of two or more superposed layers and which therefore has a larger thickness than the other portion. In this case, the operating end of the print head may contact or interfere with such a comparatively thick overlapping portion of the envelope when the print head is reciprocated along the platen during a printing operation. The overlapping portion of the envelope is soiled by the print head itself, or by a print ribbon if the printing is effected with the ribbon interposed between the print head and the envelope. Further, the envelope or the print ribbon may be damaged and the print head may be worn, due to the interference between the overlapping portion of the envelope and the print head.